Complex polymer mixtures of high density polyethylene (PE), polypropylene (PP), polystyrene (PS) and acrylonitrile-butadiene-styrene copolymer containing a polybrominated epoxy type flame retardant (ABS-Br) were thermally degraded at 450 degreesC in the presence of PVC and/or PET. It was found that besides a large amount of styrene and benzene derivatives (more than 50 wl.%), the pyrolysis oils contained about 1000 ppm nitrogen, 1000-4000 ppm bromine, 5000-5200 ppm chlorine and 800-1300 ppm oxygen, their amount and distribution depending on the composition of polymer mixture. The effect of PVC manifests especially in the early stages of decomposition while PET influenced also the late stages of the process. ABS copolymer and its flame retardant interact with both PVC and PET during thermal decomposition. (C) 2004 Elsevier Ltd. All rights reserved.